1. Field of the Invention
The present invention relates to a method for controlling an internal combustion engine which can reduce white smoke emissions at the time of starting an engine on a cold condition, i.e., immediately after a cold start.
2. Related Art
Conventionally, when starting at cold temperature in a direct fuel-injection diesel engine or the like, white smokes with pungent odors are discharged. As a countermeasure against this, there is well-known a technology for reducing white smoke by reducing the number of cylinders performing fuel injections when starting the engine and by increasing fuel injection quantities in the cylinders injecting fuels so as to increase a combustion temperature in a combustion chamber, i.e., a technology called traveling with reduced cylinders, (see for example, JP1986-258950 and JP1995-35835).
For example, the wall temperature in the combustion chamber is strongly involved in a tendency of discharging the white smoke from the direct fuel-injection diesel engine, as a cause of yielding the white smoke when starting the engine.
Specifically, the following mechanism is going to happen. Because the wall temperature in the combustion chamber is lower than the temperature during a load operation, a part of the fuels attached to the wall surface in the combustion chamber by the fuel injections are not fully evaporated, and are discharged as the white smokes without contributing the combustion. Because the gas temperature/pressure at the compression end becomes lower due to the heat loss, the combustion temperature is lowered and a part of the fuels unattached to the wall surface is unburned and discharged. While these incompletely-combusted fuels are discharged from an air-fuel with the exhaust gas, they become the white smoke with pungent odors. Therefore, two measures such as (1) not crashing the fuels into the wall surface, (2) completely combusting the fuels by raising the temperature of combustion gas become important so as to prevent the white smoke.
The flexibility of the fuel injection is increased due to the current electronic controls, so that the white smoke can be reduced using the above-mentioned measures. This is because the wall temperature in the combustion chamber is estimated by measuring the temperature of the coolant water and when the temperature of the coolant water is lower than the one on a warm-up condition, measures (correction of the water temperature) such as advancement of the injection timing can be taken according to the temperature. Thus, when a proportional relation between the temperature of the coolant water and the wall temperature in the combustion chamber is established, the correcting control of the water temperature is effective.
However, the equilibrium condition is not established, for a few minutes just after the cold start (right after the starting on the cold condition). The wall temperature in the combustion chamber is also equivalent to the temperature of the coolant water before starting and is rapidly warmed up, while the temperature of the coolant water is increased very little. In other words, the equilibrium condition is not established for a certain period of time after the starting.
It was known that the traveling with reduced cylinders is effective in reducing the white smoke, but the traveling with reduced cylinders in which the injections are performed in specific cylinders causes a bias of the temperature (a temperature difference) between the operating cylinders and the quiescent cylinder, thereby causing problems of lowering the credibility and yielding the white smoke from the quiescent cylinder when canceling the traveling with reduced cylinders.